1. Field of the Invention
The present invention relates to a propylene-based resin composition and to a film using the same.
The film of the present invention has optical characteristics, e.g. transparency and gloss, equal to those of conventional polypropylene films and is superior in low-temperature heat sealability and antiblocking property.
2. Description of the Related Art
Polypropylene has been used widely in fields of films and sheets due to its excellent transparency, heat resistance and food sanitation. In recent years, a fabrication speed of bags has been increased and a material with good low-temperature heat sealability is awaited in the field of packaging of foods and the like.
As a technique for achieving a good low-temperature heat sealability, Japan Patent No. 2882237 discloses that a polypropylene random copolymer which results from copolymerization of propylene and an xcex1-olefin or of propylene, ethylene and an xcex1-olefin performed in substantial absence of solvent by use of a Ziegler-Natta catalyst and which has specific ranges of propylene content, ethylene content, xcex1-olefin content and 20xc2x0 C. xylene-soluble fraction content and also has an increased comonomer content, and a film made of the copolymer are superior in low-temperature heat sealability. However, when the seal temperature is lowered by increasing the comonomer content, problems will arise; for example, if the comonomer content is increased to exceed a certain amount, rigidity will lower or the amount of fractions eluting in a solvent will increase, resulting in deterioration of food sanitation.
In JP, 60-166455,A and Japan Patent No. 3070419, disclosed is a polypropylene laminate film having a surface layer made of a polypropylene copolymer of a very high xcex1-olefin content. However, laminate films obtained by such techniques have a drawback of being deteriorated in view of its heat sealability by corona treatment and are problematic in that a sufficient lowering of heat seal temperature can not be achieved because too much increase of comonomer content will cause stickiness during a film forming step. Therefore, further improvement has bee awaited.
The object of the present invention is to provide a polypropylene film having optical characteristics, e.g. transparency and gloss, equal to those of conventional polypropylene films and being superior in low-temperature heat sealability and antiblocking property.
In a first aspect of the present invention, provided is a propylene-based resin composition comprising:
from 40 to 99% by weight of a propylene-based copolymer (X) consisting of from 1 to 30% by weight of component (A) that is a copolymeric component which is made up of propylene and an xcex1-olefin having 4 or more carbon atoms and which satisfies Requirement 1 defined below or a copolymeric component which is made up of propylene, an xcex1-olefin having 4 or more carbon atoms and ethylene and which satisfies Requirement 1 and Requirement 2 defined below and from 70 to 99% by weight of component (B) that is a copolymeric component which is made up of propylene and an xcex1-olefin having 4 or more carbon atoms and which satisfies Requirement 3 defined below or a copolymeric component which is made up of propylene, an xcex1-olefin having 4 or more carbon atoms and ethylene and which satisfies Requirement 3 and Requirement 4 defined below, wherein the copolymer (X) satisfies Requirement 5 defined below, and
from 1 to 60% by weight of a propylene-based copolymer (Y) made up of propylene and an xcex1-olefin and/or ethylene, the copolymer (Y) having a content of propylene of from 86 to 97% by weight and a combined content of ethylene and the xcex1-olefin of from 3 to 14% by weight, provided that each of the percentages of the amounts of the component (A) and the component (B) is based on the amount of the copolymer (X) and the sum of the percentages of the amounts of the components (A) and (B) is 100% by weight, each of the percentages of the amounts of the copolymer (X) and the copolymer (Y) is based on the combined amount of the copolymers (X) and (Y), and the content of propylene in the copolymer (Y) and the combined content of ethylene and the xcex1-olefin in the copolymer (Y) are respectively based on the combined amount of propylene, ethylene and the xcex1-olefin in the copolymer (Y):
Requirement 1: The content of xcex1-olefin having 4 or more carbon atoms in the component is not less than 1 mol % but less than 15 mol %.
Requirement 2: The content of ethylene in the component is not more than 5 mol %.
Requirement 3: The content of the xcex1-olefin having 4 or more carbon atoms in the component is from 15 mol % to 30 mol %.
Requirement 4: The content of ethylene in the component is not more than 5 mol %.
Requirement 5: In measurement of a DSC curve of the material, the amount of heat absorption within the temperature range of from Txe2x88x9210 (xc2x0 C.) to T+10 (xc2x0 C.) accounts for from 15 to 36% the amount of heat absorption within the temperature range of from 53xc2x0 C. to 170xc2x0 C., wherein T denotes a temperature (xc2x0 C.) at which a maximum endothermic peak appears.
In a second aspect, the present invention provides a propylene-based resin composition of the first aspect, wherein the copolymer (X) is a copolymer such that the component (A) is polymerized in a first step and the component (B) is polymerized in a second step or in the second and later steps performed in the presence of the component (A) which has been formed in the first step.
In a third aspect, the present invention provides a propylene-based resin composition of the second aspect, wherein the copolymer (X) is a copolymer obtained by performing the polymerization for forming the component (A) in the absence of an inert solvent and performing the polymerization for forming the component (B) in a gas phase.
In a fourth aspect, the present invention provides a propylene-based-resin-composition provided-in the first aspect, wherein the copolymer (X) is a copolymer obtained by polymerizing propylene and an xcex1-olefin having 4 or more carbon atoms or polymerizing propylene, an xcex1-olefin having 4 or more carbon atoms and ethylene in the presence of a solid catalyst component containing Ti, Mg and halogen as essential components.
In the fifth aspect, the present invention provides a film having a layer made of the propylene-based resin composition provided in the first aspect.